Your body isn't one sponge

Posted 05 July 2026 · Field Note #23

When you breathe gas under pressure, it dissolves into your tissues — but not evenly, and not all at the same speed. Blood-rich tissue like your brain loads within minutes; fatty, poorly-perfused tissue like joints and bone takes hours. A decompression model has to account for both, so it pretends your body is a set of separate buckets filling and draining at different rates.

Those buckets are tissue compartments, and each one has a half-time: how long it takes to absorb (or release) half the gas it's heading toward. Bühlmann's model uses 16 of them, from about 4 minutes to over 600. They're not anatomical organs — they're a mathematical spread chosen to cover how real human tissue behaves.

Here's why the spread matters. Fast compartments (short half-times) load and unload quickly, so they dominate short, deep dives — they're nearly full before a slow tissue has noticed you left the surface. Slow compartments (long half-times) barely move on a quick dive but keep loading through a long exposure, and they're what's still off-gassing during your surface interval and the hours after.

At any instant, whichever compartment sits closest to its own pressure limit is your leading tissue — the one driving the decision. Your computer tracks all 16 simultaneously and obeys whichever is most loaded relative to its ceiling. Early in a deep dive that's a fast tissue; late in a long or repetitive day it's a slow one. The leadership changes hands as the dive evolves.

The practical upshot: there's no single number that captures your decompression state, which is why two divers on slightly different profiles surface with different no-stop limits. Trust the computer to juggle the compartments, dive the profile you planned, and remember that the slow tissues you can't feel are exactly the ones that govern repetitive diving and flying after.

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⚠ Educational only — not a substitute for training or a dive computer. Verify every number independently and dive within your certification.